Head drum with magnetic mounting of rotary transformer

ABSTRACT

According to a first aspect the present invention is related to a head drum arrangement allowing a much easier mounting of the rotary transformer. The head drum arrangement comprises a non-rotating lower drum and a rotating upper drum, which are connected by a shaft fixed in the lower drum. The upper drum is mounted on the shaft by a bearing and preferably by two ball bearings. A rotary transformer is arranged between the lower drum and the upper drum having a fixed stator and a rotor rotating jointly with the upper drum. The rotor is non-positively held in its position by the magnetic force of a permanent magnet accommodated in the upper drum.

[0001] The present invention is related to a head drum for magnetic tapeapparatuses. The invention is based on a head drum according to theprecharacterizing clause of Patent claim 1. In the following text, amagnetic tape apparatus should be understood as meaning any apparatus inwhich signals, data or information in analogue and/or digital form arerecorded on a magnetic tape and/or read from the latter. Independentlyof this, these apparatuses may also have other functions, e.g. they maybe combined with an electronic camera. According to a second aspect thepresent invention additionally relates to a magnetic tape apparatus,which is equipped with an inventive head drum.

[0002] In general a head drum comprises a fixed lower drum and arotating upper drum, carrying at least two read/write heads in a 180°configuration on its periphery. In operation, a magnetic tape is incontact with at least half of the circumference of the head drum. Forthe sake of simplicity in the following, the read/write heads will bereferred to only as video heads reading signals from the tape. However,it is to be noted that the invention is not limited to reading videosignals.

[0003] The rotating video heads read signals from the magnetic tape,which have to be transferred to the fixed lower drum, which is connectedto signal processing circuitry. It is known to use brushes to transferthe signals between the rotating upper drum and the fixed lower drum.However, in practice the transferred signals are weak and the noisegenerated by the brushes tends to deteriorate the transferred signals.Furthermore, brushes are not reliable over long periods of time.Therefore, rotary transformers comprising a fixed stator and a rotatingrotor are utilized to transmit signals from the rotating upper drum tothe fixed lower drum are utilized in today's head drums. In today's headdrums the parts of the rotary transformer are fixed either by mechanicalmeans like screws or they are fixed by glue or cement. The firstsolution requires additional elements and machining of the members to beconnected. The second solution needs the handling of potentiallyhazardous products, e.g. fire hazardous glue. In addition this kind ofproducts usually present problems to the environment.

[0004] It is therefore desirable to provide a head drum in which therotary transformer is fixed in a simple and cost effective way.

[0005] The head drum arrangement comprises a fixed lower drum and arotating upper drum being connected by a shaft, which is fixed in thelower drum. The upper drum is mounted on the shaft by a bearing. Thearrangement further comprises a two-part rotary transformer having afixed stator associated with the lower drum and rotor rotating jointlyand associated with the upper drum. A permanent magnet is in contactwith one part of the rotary transformer such that said part is held onthe associated drum by the magnetic field of the permanent magnet. Inthis way advantageously there is no need to use hazardous materials oradditional mechanical elements.

[0006] In a specific embodiment of the invention the permanent magnet isarranged on the rotating upper drum and it is in contact with the rotorof the rotary transformer such that the rotor is held on the upper drumby the magnetic field of the permanent magnet. A compact structure ofthe head drum is achievable if the permanent magnet is accommodated in arecess of the upper drum.

[0007] The structure of the inventive head drum is particularly simpleif the recess to accommodate the magnet is formed by the seat of thebearing. In this case it is possible to support the magnet by therotating outer ring of the bearing.

[0008] It is necessary to avoid any interference between the magneticfields associated with the read/write heads of the head drum and themagnetic fields of the tape on the one hand and the magnetic field ofthe permanent magnet on the other hand. Therefore, in another embodimentof the invention the permanent magnet is mounted close to the rotationaxis and remote from the magnetic heads mounted on the circumference ofthe upper drum.

[0009] For the same reasons the magnetization of the permanent magnet isselected such that the rotor is securely held on the upper drum and themagnetic field of the permanent magnet is too weak to alter data storedon a magnetic medium or influence signals read or written by themagnetic heads.

[0010] To simplify the assembly of the head drum arrangement it ispossible to provide the permanent magnet with a structural elementacting as a centering means for the one part of the rotary transformer,which is held by the magnetic field of the permanent magnet.

[0011] According to a second aspect of the invention a magnetic taperecorder is provided, which is equipped with an inventive head drumarrangement.

[0012] The invention can be better understood by reading the followingdescription in connection with the accompanying drawing. In the drawing

[0013]FIG. 1a shows a head drum arrangement according to the invention,and

[0014]FIG. 1b shows a partial view of FIG. 1a in an enlarged scale.

[0015] In FIG. 1a the reference number 1 refers to the head drumarrangement as a whole. The head drum 1 comprises a fixed or lower drum2 and a rotating or upper drum 3. The upper drum 3 carries on itsperiphery a pair of read/write heads in a 180° configuration, which arenot shown in FIG. 1a. The head drum 1 can be adapted to accommodate ahigher number of read/write heads, e.g. four or six heads depending onthe concrete application of the head drum. The signals read by thereading heads are transmitted from the rotating upper drum to the fixedlower drum via a rotary transformer 4. In a similar way the signals tobe written by the write heads are transmitted by the rotary transformer4 from the lower drum 2 to the upper drum 3. The lower drum 2 and theupper drum 3 are mounted on a shaft 6, which is fixed in the lower drum2. The upper drum 3 is mounted on the shaft 6 by means of two ballbearings 7 a, 7 b, both having an inner ring 8 a, 8 b and an outer ring9 a, 9 b. The outer rings 9 a, 9 b are accommodated in the upper drum 3in circular seats 11 a, 11 b, which are connected by a bore 12, having asmaller diameter than the seats 11 a, 11 b. The bore 12 creates two ringshaped shoulders 13 a, 13 b serving as support or bearing for the outerrings 9 a, 9 b of the ball bearings.

[0016] The following description refers to both FIG. 1a and FIG. 1b.

[0017] The rotary transformer 4 includes a stator 16 and a rotor 17. Thestator 16 rests on a hub 19, which is one piece with the lower drum 2.The hub 19 is ring shaped having a recess 21 to accommodate a cable,e.g. a Flexible Printed Cable (FPC) to connect the stator with signalprocessing circuits. The hub 19 continues as a collar 20. The innersurface of collar 20 is in contact with the shaft 6 and its outersurface is in contact with the inner surface of stator 16. The collar 20effectively centers the stator 16 on the lower drum 2. The stator 16 issecurely fixed on the hub 19, e.g. by glue or other conventional meansknown in the art.

[0018] Contrary to that the rotor 17 rests on a ring shaped hub 22. Itis noted that the rotor 17 is neither glued on to the hub nor positivelyfixed by mechanical elements. The rotor 17 is rather non-positivelymaintained in the shown position by a circular permanent magnet 23located in a ring shaped recess 24 between the rotor 17 and the ballbearing 7 b. The thickness of the magnet 23 is reduced at a certaindistance from the outer periphery of the magnet in radial directiondefining an outer portion 25 and an inner portion 26 of the magnet (FIG.1b). Only the outer portion 25 of the magnet 23 is in contact with therotating outer ring 9 b of a ball bearing 7 b. Hence the magnet does notcause any friction.

[0019] The magnet 23 generates a permanent magnetic field effective toattract the magnet 23 to the other ring 9 b of a bearing 7 a and toattract the rotor 17 to the magnet 23. The rotor 17 is in contact withthe ring shaped hub 22 and is pressed against it by the attractive forcegenerated by the magnet. In this way a non-positive connection betweenthe rotor 17 and the hub 22 is established. The upper face in FIG. 1b ofthe magnet 23 is in contact with the lower face of rotor 17. The innerportion 26 is provided with a ring shaped shoulder 27. The outersidewall of the shoulder 27 is in contact with the inner circularsurface of the rotor 17. In this way the shoulder 27 of the magnet 23serves as a centering means for the rotor 17. The non-positiveconnection is sufficient to securely maintain the rotor 17 at its properposition. At the same time the magnetic field of the permanent magnetdoes not disturb or deteriorate the magnetization of the magnetic tapeduring recording or play back. Similarly, the signals read or recordedby the read/write heads are not influenced by the magnetic field of thepermanent magnet 23.

[0020] Between the stator 16 and the rotor 17 there is a gap of 30 to 40micrometers with a tolerance of ±10 micrometers, which is only visiblein FIG. 1b. The value of the gap is determined by in a conventional way,e.g. a spacer. The whole arrangement is securely held together by a discor preload brass 28, which is fixed on the shaft 6. The disc 28 appliesa pressure against the inner rings 8 a, 8 b of bearings 7 a, 7 b. Thepressure is generated by threading the disc 28 on the shaft 6 or bythreading a nut, which is not shown in FIG. 1a.

[0021] The upper drum is driven by a motor, which is not shown in FIG.2. The rotor of the motor is drivingly connected to the upper drum by ascrew to be fixed in a threaded hole 29.

[0022] It is evident, that the invention is also applicable to othertypes of head drums, e.g. those having an upper drum, which is driven bya shaft. The inventive head drum can be utilized in any kind of magnetictape apparatus.

[0023] Reference Numbers

[0024]1 head drum arrangement

[0025]2 lower drum

[0026]3 upper drum

[0027]4 rotary transformer

[0028]5

[0029]6 shaft

[0030]7 a, 7 b ball bearing

[0031]8 a, 8 b inner ring

[0032]9 a, 9 b outer ring

[0033]10

[0034]11 a, 11 b seat

[0035]12 bore

[0036]13 a, 13 b ring shaped shoulder

[0037]14

[0038]15

[0039]16 stator

[0040]17 rotor

[0041]18

[0042]19 hub

[0043]20 collar

[0044]21 recess

[0045]22 hub

[0046]23 magnet

[0047]24 recess

[0048]25 outer portion of magnet

[0049]26 inner portion of magnet

[0050]27

[0051]28 disk

[0052]29 threaded hole

1. Head drum arrangement comprising a fixed lower drum (2) and a rotating upper drum (3) being connected by a shaft (6) fixed in the lower drum (2), wherein the upper drum (3) is mounted on the shaft by a bearing (7 a, 7 b), wherein the arrangement further comprises a two-part rotary transformer (4) having a fixed stator (16) associated with the lower drum and a rotor (17) rotating jointly and associated with the upper drum characterized in that a permanent magnet (23) is in contact with one part of the rotary transformer (17) such that said part is held on the associated drum (3) by the magnetic field of the permanent magnet (23).
 2. Head drum arrangement according to claim 1 characterized in that a permanent magnet (23) arranged on the rotating upper drum (3) is in contact with the rotor (17) of the rotary transformer (4) such that the rotor is held on the upper drum by the magnetic field of the permanent magnet.
 3. Head drum arrangement according to claim 1 characterized in that the permanent magnet (23) is accommodated in a recess (24) of the upper drum (3).
 4. Head drum arrangement according to claim 3 characterized in that the recess (24) of the upper drum (3) is formed by seat (11 b) of the bearing (7 b).
 5. Head drum arrangement according to claim 1 characterized in that the permanent magnet is supported by the rotating ring (9 b) of the bearing (7 b).
 6. Head drum arrangement according to claim 1 characterized in that the permanent magnet (23) is mounted close to the rotation axis and remote from the magnetic heads mounted on the circumference of the upper drum (3).
 7. Head drum arrangement according to claim 1 characterized in that the magnetization of the permanent magnet (23) is selected such that the rotor (17) is securely held on the upper drum and the magnetic field of the permanent magnet is too weak to alter data stored on a magnetic medium or influence signals read or written by the magnetic heads.
 8. Head drum arrangement according to claim 1 characterized in that the permanent magnet (23) is provided with a structural element (27) acting as a centering means for said one part (17) of the rotary transformer (4).
 9. Magnetic tape recorder equipped with a drum arrangement according to claim 1 or several of claims 1 to
 8. 